Intracavernous injection therapy is direct injection of a small amount of drug into the corpora cavernosa of a penis. The drug can comprise smooth muscle relaxants that can help increase blood flow into the penis. The advantage of injection therapy is that it does not depend on oral absorption, as pills do.
Currently, the only FDA-approved chemicals for intracavernous injection therapy are Caverject® alprostadil for injection (Pfizer) and Edex® alprostadil for injection from Actient Pharmaceuticals. Both of these agents are prostaglandin E1. Other agents used alone or in combination are papaverine and phentolamine. All three—prostaglandin E1, papaverine, and phentolamine—may be used in combination, and the combination is referred to as “triple P” or “trimix.” Prostaglandin E1 and triple P are the two most common forms of injection therapy.
The needle used for the injection is small (typically between about 27-31 gauge) and short. The needle does not need to pierce deeply into the penis to be effective, just into the corpora on one side (e.g., left or right side). The syringe used with the needle is also typically small because the injection volume is usually 1 cc or less. After an initial test dose, usually carried out by the urologist, the urologist will decide on a dose that a patient will use at home (via self-injection or with the help of a partner). It is recommended that the injection not be used more frequently than every 48-72 hours and that successive injections be given to alternate sides of the corpora cavernosa.